Photolithography is a commonly-used method for patterning features during semiconductor processing. A photosensitive material (photoresist) is formed over a mass which is ultimately to be patterned, and the photoresist is subsequently subjected to radiation. The radiation is provided in a pattern so that some portions of the photoresist are impacted by the radiation while other portions of the photoresist are not impacted by the radiation. The photoresist is then subjected to developing conditions which selectively remove either the impacted or non-impacted portions. If the photoresist is a positive photoresist, the impacted portions are selectively removed; and if the photoresist is a negative photoresist, the non-impacted portions are selectively removed.
The photoresist remaining after the development defines a patterned mask. The pattern of the mask can subsequently be transferred to the underlying mass utilizing appropriate etching conditions to form patterned features within the mass.
A difficulty which can be encountered during photolithographic processing is that the radiation utilized to pattern the photoresist (typically light) can be reflected from the underlying mass to cause various constructive and destructive interference patterns to occur in the light as it passes through the photoresist. This can adversely affect a pattern ultimately developed in the photoresist.
The problem is typically addressed by providing an antireflective coating immediately beneath the photoresist. Various antireflective coatings have been developed, with a deposited antireflective coating (DARC) being exemplary. Deposited antireflective coatings will typically comprise silicon and nitrogen, and can, for instance, consist of, or consist essentially of, silicon, nitrogen and optionally, hydrogen. DARC's can alternatively comprise silicon, oxygen, and in some cases, hydrogen, and can be referred to as silicon oxynitride materials.
DARC materials can be particularly useful as antireflective coatings during photolithographic processing of metals, and/or insulative materials (with an exemplary insulative material being borophosphosilicate glass).
An exemplary photolithographic fabrication process utilizing a DARC material is described with reference to FIGS. 1 and 2. Referring initially to FIG. 1, a fragment of a semiconductor construction 10 is illustrated at a preliminary processing stage. Construction 10 comprises a substrate 12. Substrate 12 can include, for example, a semiconductive material (such as, for example, monocrystalline silicon). To aid in interpretation of the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
A mass 14 is supported by substrate 12. Mass 14 can comprise an insulative material (such as, for example, borophosphosilicate glass) and/or various metals and/or metal compounds. Mass 14 is shown as a single uniform layer, but it is to be understood that mass 14 can comprise stacks of various materials.
An antireflective coating layer 16 is shown formed over mass 14. Layer 16 will preferably comprise a DARC, such as, for example, silicon oxynitride.
A photoresist 18 is shown formed over and physically against antireflective coating 16.
Radiation 20 is shown impacting various regions of photoresist 18. Radiation 20 will typically comprise light, and can, for example, predominately comprise light having a wavelength which is in the region of from about 150 nanometers to about 250 nanometers. Regions of photoresist 18 impacted by radiation 20 are illustrated generally with the label 22, and regions of the photoresist 18 which are not impacted by radiation 20 are illustrated generally. with the label 24.
Photoresist 18 can comprise a chemically amplified photoresist. In such application, radiation 20 will create a photogenerated catalyst (typically a strong acid) within regions 22 of the photoresist. The photoresist is then subjected to a post-exposure bake wherein the photogenerated catalyst causes further reactions to alter solubility of exposed regions 22 (and in some applications regions proximate exposed regions 22) relative to regions 24 in a developer solution. An advantage of utilizing chemically amplified photoresists is that such can increase the sensitivity of photoresist to radiation by enabling a single incident photon to be responsible for many chemical events.
Photoresist 18 can be referred to as a photoresist system to indicate that the photoresist can comprise various components ultimately affected by exposure of a portion of photoresist 18 to light. For instance, if material 18 comprises a chemically amplified photoresist system, it will typically comprise a photoactive species which ultimately forms a photocatalyst (typically an acid) upon exposure to light having a suitable wavelength. The photoactive species then interacts with other materials present in the photoresist system to alter chemical properties of the system. The material 18 can be referred to as consisting essentially of a photoresist system to indicate that the material 18 consists essentially of components which are patterned during a photolithographic process to form a mask. Photoresist system 18 can, in particular applications, comprise a multilayer resist.
FIG. 2 illustrates construction 10 after a suitable post-exposure bake, and subsequent exposure to a developing solution. Photoresist 18 is illustrated as being a positive photoresist, and accordingly impacted regions 22 (FIG. 1) are selectively removed relative to non-impacted regions 24.
A problem with utilization of DARC is that such can scavenge photogenerated catalysts (such as acid) during the post-exposure bake of photoresist 18, and can accordingly interfere with the patterning of the photoresist. For instance, the patterned photoresist of FIG. 2 is shown to comprise blocks 30 and 32 and such blocks are wider proximate antireflective coating 16 than at upper surfaces of the blocks. The widened regions at the blocks can be referred to as foot portions 34. Such foot portions are undesired.
It would be desirable to develop photolithographic processing methods which alleviate or prevent formation of foot portions 34.